Passive Cooling online!
With a very nice day on Sunday and the threat of the first real week of heat, I took some time on Father's Day and opened up the passive cooling intakes. I closed most of the windows this morning except the window at the very top of the house and we shall see how it works when we get home tonight.
This is a very low tech solution: Basically, we have two runs of 4" PVC pipe that pop out of the ground at the back of the house. I added two elbows at the end of each run and a mesh to keep out unwanted guests. The runs go down to almost the drainage tile and run beside the foundation, in the ground along the whole length of the house on the west side. One run then heads through the foundation and up, inside the wall to a grill in my son's room. The other run doubles back and up into the master bed room.
The concept is all based on the "stack effect" where hot air builds up at the top of the house and looks for a way out. With the roof window open, hot air escapes, creating low pressure in the house. Because our house is very well sealed, only the HRV and the passive cooling system offer a way for new air to get into the house. The HRV system continues to run, so it should mean that quite a bit of new fresh air would come in via those 4" runs. As the air is drawn through the pipe, the cool earth will take some of the heat out of the air (and likely a bit of the moisture) and delivery cooler air to the upstairs bedrooms, where it is needed most.
With no mechanical parts, we are hopefully it will be a good, no-energy solution to keeping the house cooler this summer.
Tom the Radon Guy: If you haven't already done so since the addition of the vent pipes, please test your home for Radon Gas. You could very well be drawing this radioactive gas into your home. Testing is simple and very inexpensive. Radon Gas is the second leading cause of lung cancer, second only to smoking. (07/16/09)
PM: Tom, thank you for your comments. I have had the question of Radon Gas asked a few times in the build, and particularly depending on where you are building a house and/or the construction of the house Radon Gas is a consideration. In our case, however, I have a few good reason not to be concerned about Radon Gas build up in our house. Firstly, the passive cooling intake pipes are glued and sealed PVC pipe (the same used for waste water). Being air impermeable and air pressure neutral, there is no high risk of increased amounts of Radon Gas penetrating the pipes from the soil. In addition, the pipes are all sealed as they come through the foundation so there are no cracks and fissures, which is the usual vector for Radon Gas. Our foundation construction is concrete footings with exterior sealed block walls and a poured concrete slab floor (with our radiant heating in it, by the way). Between the concrete floor and the dirt is a vapour barrier, again reducing the risk of Radon Gas penetration. Lastly, the house has a HRV system, which is required to keep refreshing the air in the house. The air in the basement is recirculated as often as the rest of the house, which avoids pockets of stale, trapped air. Basements that have areas or rooms where the air is trapped has a higher potential for Radon Gas build up. In short, I think we are pretty safe. If readers would like to know more about Radon Gas and health concerns in Canada, there is a great site provided by the Government of Canada that can answer some of your questions. You can also get a lot of details on Wikipedia on Radon. If you are really concerned, contact your local government health department or municipal planning department and they should be able to point you in the right direction. (07/17/09)
Mike Manning: I am interested in incorporating a passive cooling system like the one in your home in a house I have under construction in Bronte Village. My question is what do you think about installing an in-line fan to circulate the air into a root cellar in the basement? What do you think of a second loop that is hooked up to an air handling system that would circulate the air through the house? (10/10/09)
PM: It turned out that fans were a must. We found fans that fit in the register outlets and they worked very well, but a bit noisier than we would have liked. What you suggest sounds good, as long as you make sure you aren't creating a moisture imbalance in the house. Our cooling vents go right into the upstairs. My only question about what you are proposing would be are you going to end up introducing too much moisture into your basement... If you have an effective HRV this shouldn't be an issue. I hope it works well for you. (10/11/09)